The invention relates to a height adjustment mechanism for a chair and more particularly, to a height adjustment mechanism such as for a chair back.
Conventional office chairs typically have a seat assembly as well as a back assembly which extends upwardly from a rear edge of the seat for respectively supporting the seat and back of the chair occupant. The seat assembly typically includes a rigid upright and the back assembly is supported on the upright. Also, such chairs often include a pair of chair arms which extend upwardly from the opposite side edges of the seat assembly for supporting the occupant""s arms.
In a continuing effort to provide more comfortable office chairs, many of the chair components are adjustable in various directions so that the components of the chair more closely conform to and comfortably support the seat, arms and back of the occupant. In this regard, it is well known to provide a height adjusting mechanism in the back assembly of the chair which permits the height of the chair to be adjusted relative to the seat assembly. Height adjusting mechanisms also are known to be provided in chair arms to permit vertical adjustment thereof.
With respect to such height adjusting mechanisms and primarily those height-adjusting mechanisms used in the back assembly, many of these mechanisms include ratchet-like mechanisms having a vertically elongate row of teeth, which define a rack, and a pawl which engages the rack. These ratchet mechanisms permit the back assembly to be manually lifted upwardly along the upright wherein the mechanism maintains the back assembly at a selected elevation when the occupant releases the back assembly.
Many of these mechanisms include actuator parts such as levers, pins and the like which act on the pawl when the back assembly is at the upper limit of vertical travel to separate the pawl from the rack and permit downward sliding, i.e. manual lowering of the back assembly to a lowered position. Such height adjusting mechanisms further include actuator parts at the lower end of travel which automatically disengage the lever, pins or the like to release the pawl and permit the pawl to reengage the rack.
Examples of such height adjusting mechanisms are disclosed in U.S. Pat. Nos. 2,405,013, 4,639,039, 5,560,233, 5,649,741 and 5,685,609.
Additionally, it is known to provide gears in a height-adjusting mechanism wherein the gear cooperates with a lock operated by a manual actuator to release and lock the gear which respectively permits and prevents upward movement of a furniture component. An example of one such mechanism is disclosed in U.S. Pat. No. 3,194,187.
It is an object of the invention to provide an inventive height adjusting mechanism which is improved relative to such prior height adjusting mechanisms.
The height adjusting mechanism of the invention is connected between a rigid upright extending upwardly from the seat assembly and an inner shell of the back assembly. The inventive height adjusting mechanism includes a rack plate on one of the back assembly and upright and a gear rotatably supported on the other of the back assembly and upright.
The gear engages the teeth of a vertical rack on the rack plate and rolls along the rack during raising and lowering of the back assembly. The height adjustment assembly includes a lock member that removably engages the gear to prevent rotation of the gear which thereby prevents relative vertical movement of the rack plate since the rack teeth mate with the gear teeth. However, lifting of the back assembly by the chair occupant causes the lock member and the gear to continuously or intermittently separate to allow the gear to roll along the rack. If the back assembly is released, the back assembly tends to want to fall at which time the lock member reengages the gear and prevents rotation thereof.
To permit lowering of the back assembly, the height adjustment mechanism further includes a movable disengagement member which is actuated to separate the gear and lock member at an upper limit of travel and maintains the gear and lock member separated as the back assembly is lowered. The gear is free to roll along the rack during this lowering movement.
At the lower limit of travel, the disengagement member is automatically actuated to permit reengagement of the lock member and the gear. When the lock member and gear are reengaged, the back assembly may be moved upwardly but the cooperating lock member and gear continue to prevent downward movement of the back assembly.
Multiple embodiments of the height adjustment mechanism are disclosed herein. It will be understood that other objects and purposes of the invention, and variations thereof, will be apparent upon reading the following specification and inspecting the accompanying drawings.